Identification of a novel nonstructural protein, VP9, from white spot syndrome virus: its structure reveals a ferredoxin fold with specific metal binding sites

MRF: a tool to overcome the barrier of inconsistent genome annotations and perform comparative genomics studies for the largest animal DNA virus

BACKGROUND

The genome of the largest known animal virus, the white spot syndrome virus (WSSV) responsible for huge economic losses and loss of employment in aquaculture, suffers from inconsistent annotation nomenclature. Novel genome sequence, circular genome and variable genome length led to nomenclature inconsistencies. Since vast knowledge has already accumulated in the past two decades with inconsistent nomenclature, the insights gained on a genome could not be easily extendable to other genomes. Therefore, the present study aims to perform comparative genomics studies in WSSV on uniform nomenclature.

METHODS

We have combined the standard mummer tool with custom scripts to develop missing regions finder (MRF) that documents the missing genome regions and coding sequences in virus genomes in comparison to a reference genome and in its annotation nomenclature. The procedure was implemented as web tool and in command-line interface. Using MRF, we have documented the missing coding sequences in WSSV and explored their role in virulence through application of phylogenomics, machine learning models and homologous genes.

RESULTS

We have tabulated and depicted the missing genome regions, missing coding sequences and deletion hotspots in WSSV on a common annotation nomenclature and attempted to link them to virus virulence. It was observed that the ubiquitination, transcription regulation and nucleotide metabolism might be essentially required for WSSV pathogenesis; and the structural proteins, VP19, VP26 and VP28 are essential for virus assembly. Few minor structural proteins in WSSV would act as envelope glycoproteins. We have also demonstrated the advantage of MRF in providing detailed graphic/tabular output in less time and also in handling of low-complexity, repeat-rich and highly similar regions of the genomes using other virus cases.

CONCLUSIONS

Pathogenic virus research benefits from tools that could directly indicate the missing genomic regions and coding sequences between isolates/strains. In virus research, the analyses performed in this study provides an advancement to find the differences between genomes and to quickly identify the important coding sequences/genomes that require early attention from researchers. To conclude, the approach implemented in MRF complements similarity-based tools in comparative genomics involving large, highly-similar, length-varying and/or inconsistently annotated viral genomes.

Investigation of the New Inhibitors by Sulfadiazine and Modified Derivatives of α-D-glucopyranoside for White Spot Syndrome Virus Disease of Shrimp by In Silico: Quantum Calculations, Molecular Docking, ADMET and Molecular Dynamics Study

The α-D-glucopyranoside and its derivatives were as the cardinal investigation for developing an effective medication to treat the highest deadly white spot syndrome virus (WSSV) diseases in Shrimp. In our forthcoming work, both computational tools, such as molecular docking, quantum calculations, pharmaceutical kinetics, ADMET, and their molecular dynamics, as well as the experimental trial against WSSV, were executed to develop novel inhibitors. In the beginning, molecular docking was carried out to determine inhibitors of the four targeted proteins of WSSV (PDB ID: 2ED6, 2GJ2, 2GJI, and 2EDM), and to determine the binding energies and interactions of ligands and proteins after docking. The range of binding affinity was found to be between −5.40 and −7.00 kcal/mol for the protein 2DEM, from −5.10 to 6.90 kcal/mol for the protein 2GJ2, from −4.70 to −6.2 kcal/mol against 2GJI, and from −5.5 kcal/mol to −6.6 kcal/mol for the evolved protein 2ED6 whereas the L01 and L03 display the highest binding energy in the protein 2EDM. After that, the top-ranked compounds (L01, L02, L03, L04, and L05), based on their high binding energies, were tested for molecular dynamics (MD) simulations of 100 ns to verify the docking validation and stability of the docked complex by calculating the root mean square deviation (RMSD) and root mean square fluctuation (RMSF). The molecules with the highest binding energy were then picked and compared to the standard drugs that were been applied to fish experimentally to evaluate the treatment at various doses. Consequently, approximately 40–45% cure rate was obtained by applying the dose of oxytetracycline (OTC) 50% with vitamin C with the 10.0 g/kg feed for 10 days. These drugs (L09 to L12) have also been executed for molecular docking to compare with α-D-glucopyranoside and its derivatives (L01 to L08). Next, the evaluation of pharmacokinetic parameters, such as drug-likeness and Lipinski’s principles; absorption; distribution; metabolism; excretion; and toxicity (ADMET) factors, were employed gradually to further evaluate their suitability as inhibitors. It was discovered that all ligands (L01 to L12) were devoid of hepatotoxicity, and the AMES toxicity excluded L05. Additionally, all of the compounds convey a significant aqueous solubility and cannot permeate the blood-brain barrier. Moreover, quantum calculations based on density functional theory (DFT) provide the most solid evidence and testimony regarding their chemical stability, chemical reactivity, biological relevance, reactive nature and specific part of reactivity. The computational and virtual screenings for in silico study reveals that these chosen compounds (L01 to L08) have conducted the inhibitory effect to convey as a possible medication against the WSSV than existing drugs (L09, L10, L11 and L12) in the market. Next the drugs (L09, L10, L11 and L12) have been used in trials.

White spot syndrome viral protein VP9 alters the cellular higher-order chromatin structure

Viral protein 9 (VP9) is a non-structural protein of white spot syndrome virus (WSSV) highly expressed during the early stage of infection. The crystal structure of VP9 suggests that the polymers of VP9 dimers resemble a DNA mimic, but its function remains elusive. In this study, we demonstrated that VP9 impedes histones binding to DNA via single-molecule manipulation. We established VP9 expression in HeLa cells due to the lack of a WSSV-susceptible cell line, and observed abundant VP9 in the nucleus, which mirrors its distribution in the hemocytes of WSSV-infected shrimp. VP9 expression increased the dynamics and rotational mobility of histones in stable H3-GFP HeLa cells as revealed by fluorescent recovery after photobleaching and fluorescence anisotropy imaging, which suggested a loosened compaction of chromatin structure. Successive salt fractionation showed that a prominent population of histones was solubilized in high salt concentrations, which implies alterations of bulk chromatin structure. Southern blotting identified that VP9 alters juxtacentromeric chromatin structures to be more accessible to micrococcal nuclease digestion. RNA microarray revealed that VP9 expression also leads to significant changes of cellular gene expression. Our findings provide evidence that VP9 alters the cellular higher-order chromatin structure, uncovering a potential strategy adopted by WSSV to facilitate its replication.

WSV152 induces apoptosis and promotes viral replication in Litopenaeus vannamei

Previous studies have indicated that white spot syndrome virus (WSSV) infection induces apoptosis in many shrimp organs. However, the mechanism by which WSSV causes host apoptosis remains largely unknown. In this study, we demonstrated the function of wsv152, the first mitochondrial protein identified as encoded by WSSV. Glutathione S-transferase pulldown and co-immunoprecipitation analysis revealed that wsv152 interacts with the shrimp mitochondrial protein cytochrome c oxidase 5a (COX5a), a subunit of the COX complex. We also found that wsv152 expression significantly increased the rate of apoptosis, suggesting a role of wsv152 in WSSV-induced apoptosis in shrimp. Knockdown of wsv152 in vivo led to downregulation of several apoptosis-related shrimp genes, including cytochrome c, apoptosis-inducing factor and caspase-3. Suppression of wsv152 also resulted in significant reductions in the number of WSSV genome copies in tissues and in the mortality of WSSV-infected shrimp. Together, these results suggest that wsv152 targets host COX5a and is associated with the expression profiles of apoptosis-related shrimp genes. Wsv152 is likely also involved in WSSV-induced apoptosis, thereby facilitating virus infection and playing a complex role in WSSV pathogenesis.

Characterization of putative proteins encoded by variable ORFs in white spot syndrome virus genome

Background

White Spot Syndrome Virus (WSSV) is an enveloped double-stranded DNA virus which causes mortality of several species of shrimp, being considered one of the main pathogens that affects global shrimp farming. This virus presents a complex genome of ~ 300 kb and viral isolates that present genomes with great identity. Despite this conservation, some variable regions in the WSSV genome occur in coding regions, and these putative proteins may have some relationship with viral adaptation and virulence mechanisms. Until now, the functions of these proteins were little studied. In this work, sequences and putative proteins encoded by WSSV variable regions were characterized in silico.

Results

The in silico approach enabled determining the variability of some sequences, as well as the identification of some domains resembling the Formin homology 2, RNA recognition motif, Xeroderma pigmentosum group D repair helicase, Hemagglutinin and Ankyrin motif. The information obtained from the sequences and the analysis of secondary and tertiary structure models allow to infer that some of these proteins possibly have functions related to protein modulation/degradation, intracellular transport, recombination and endosome fusion events.

Conclusions

The bioinformatics approaches were efficient in generating three-dimensional models and to identify domains, thereby enabling to propose possible functions for the putative polypeptides produced by the ORFs wsv129, wsv178, wsv249, wsv463a, wsv477, wsv479, wsv492, and wsv497.

Electronic supplementary material

The online version of this article (10.1186/s12900-019-0106-y) contains supplementary material, which is available to authorized users.

Crustacean Genome Exploration Reveals the Evolutionary Origin of White Spot Syndrome Virus

White spot syndrome virus (WSSV) is a crustacean-infecting, double-stranded DNA virus and is the most serious viral pathogen in the global shrimp industry. WSSV is the sole recognized member of the family Nimaviridae, and the lack of genomic data on other nimaviruses has obscured the evolutionary history of WSSV. Here, we investigated the evolutionary history of WSSV by characterizing WSSV relatives hidden in host genomic data. We surveyed 14 host crustacean genomes and identified five novel nimaviral genomes. Comparative genomic analysis of Nimaviridae identified 28 "core genes" that are ubiquitously conserved in Nimaviridae; unexpected conservation of 13 uncharacterized proteins highlighted yet-unknown essential functions underlying the nimavirus replication cycle. The ancestral Nimaviridae gene set contained five baculoviral per os infectivity factor homologs and a sulfhydryl oxidase homolog, suggesting a shared phylogenetic origin of Nimaviridae and insect-associated double-stranded DNA viruses. Moreover, we show that novel gene acquisition and subsequent amplification reinforced the unique accessory gene repertoire of WSSV. Expansion of unique envelope protein and nonstructural virulence-associated genes may have been the key genomic event that made WSSV such a deadly pathogen.IMPORTANCE WSSV is the deadliest viral pathogen threatening global shrimp aquaculture. The evolutionary history of WSSV has remained a mystery, because few WSSV relatives, or nimaviruses, had been reported. Our aim was to trace the history of WSSV using the genomes of novel nimaviruses hidden in host genome data. We demonstrate that WSSV emerged from a diverse family of crustacean-infecting large DNA viruses. By comparing the genomes of WSSV and its relatives, we show that WSSV possesses an expanded set of unique host-virus interaction-related genes. This extensive gene gain may have been the key genomic event that made WSSV such a deadly pathogen. Moreover, conservation of insect-infecting virus protein homologs suggests a common phylogenetic origin of crustacean-infecting Nimaviridae and other insect-infecting DNA viruses. Our work redefines the previously poorly characterized crustacean virus family and reveals the ancient genomic events that preordained the emergence of a devastating shrimp pathogen.

Molecular Mechanisms of White Spot Syndrome Virus Infection and Perspectives on Treatments

Since its emergence in the 1990s, White Spot Disease (WSD) has had major economic and societal impact in the crustacean aquaculture sector. Over the years shrimp farming alone has experienced billion dollar losses through WSD. The disease is caused by the White Spot Syndrome Virus (WSSV), a large dsDNA virus and the only member of the Nimaviridae family. Susceptibility to WSSV in a wide range of crustacean hosts makes it a major risk factor in the translocation of live animals and in commodity products. Currently there are no effective treatments for this disease. Understanding the molecular basis of disease processes has contributed significantly to the treatment of many human and animal pathogens, and with a similar aim considerable efforts have been directed towards understanding host-pathogen molecular interactions for WSD. Work on the molecular mechanisms of pathogenesis in aquatic crustaceans has been restricted by a lack of sequenced and annotated genomes for host species. Nevertheless, some of the key host-pathogen interactions have been established: between viral envelope proteins and host cell receptors at initiation of infection, involvement of various immune system pathways in response to WSSV, and the roles of various host and virus miRNAs in mitigation or progression of disease. Despite these advances, many fundamental knowledge gaps remain; for example, the roles of the majority of WSSV proteins are still unknown. In this review we assess current knowledge of how WSSV infects and replicates in its host, and critique strategies for WSD treatment.

The VP37-binding protein F1ATP synthase β subunit involved in WSSV infection in shrimp Litopenaeus vannamei

To investigate the interaction between white spot syndrome virus (WSSV)-VP37 and gill membrane proteins (GMPs) of Pacific white shrimp (Litopenaeus vannamei), the VP37 protein was expressed and purified, and a distinct 53 kDa VP37-binding protein band was identified in GMPs by virus overlay protein binding assay and GST pull-down assay. By electroelution, the VP37 binding protein was purified and identified as F(1)ATP synthase β (F(1)ATPase β) subunit by Mass Spectrometry. The purified F(1)ATPase β subunit was used to immunize BALB/C mice to produce monoclonal antibodies (Mabs). After cell fusion, sixteen hybridomas secreting Mabs against F(1)ATPase β subunit of L. vannamei were screened by enzyme-linked immunosorbant assay (ELISA), three of which designated as 1D5, 1E8 and 2H4 were cloned by limiting dilution and further characterized by indirect immunofluorescence assay (IIFA) and western blotting. The results of IIFA showed that specific fluorescence signals located at the peripheral zone of the gills of L. vannamei. Western blotting demonstrated that three Mabs reacted specifically with the 53 kDa protein band in GMPs of L. vannamei. By IIFA, the Mabs could also cross-react with the gill cells of three other WSSV-susceptible shrimps Fenneropenaeus chinensis, Penaeus monodon and Marsupenaeus japonicus. Furthermore, the three anti-F(1)ATPase β subunit Mabs could partially block the binding of WSSV to GMPs by ELISA in vitro, and also exhibited direct anti-WSSV activity in shrimp by neutralization assay in vivo. These findings suggested that F(1)ATPase β subunit involved in WSSV infection in L. vannamei.

PROTEOMICS in aquaculture: applications and trends

Over the last forty years global aquaculture presented a growth rate of 6.9% per annum with an amazing production of 52.5 million tonnes in 2008, and a contribution of 43% of aquatic animal food for human consumption. In order to meet the world's health requirements of fish protein, a continuous growth in production is still expected for decades to come. Aquaculture is, though, a very competitive market, and a global awareness regarding the use of scientific knowledge and emerging technologies to obtain a better farmed organism through a sustainable production has enhanced the importance of proteomics in seafood biology research. Proteomics, as a powerful comparative tool, has therefore been increasingly used over the last decade to address different questions in aquaculture, regarding welfare, nutrition, health, quality, and safety. In this paper we will give an overview of these biological questions and the role of proteomics in their investigation, outlining the advantages, disadvantages and future challenges. A brief description of the proteomics technical approaches will be presented. Special focus will be on the latest trends related to the aquaculture production of fish with defined nutritional, health or quality properties for functional foods and the integration of proteomics techniques in addressing this challenging issue.

White spot syndrome virus: an overview on an emergent concern

Viruses are ubiquitous and extremely abundant in the marine environment. One of such marine viruses, the white spot syndrome virus (WSSV), has emerged globally as one of the most prevalent, widespread and lethal for shrimp populations. However, at present there is no treatment available to interfere with the unrestrained occurrence and spread of the disease. The recent progress in molecular biology techniques has made it possible to obtain information on the factors, mechanisms and strategies used by this virus to infect and replicate in susceptible host cells. Yet, further research is still required to fully understand the basic nature of WSSV, its exact life cycle and mode of infection. This information will expand our knowledge and may contribute to developing effective prophylactic or therapeutic measures. This review provides a state-of-the-art overview of the topic, and emphasizes the current progress and future direction for the development of WSSV control strategies.

White spot syndrome virus protein ICP11: A histone-binding DNA mimic that disrupts nucleosome assembly

White spot syndrome virus (WSSV) is a large ( approximately 300 kbp), double-stranded DNA eukaryotic virus that has caused serious disease in crustaceans worldwide. ICP11 is the most highly expressed WSSV nonstructural gene/protein, which strongly suggests its importance in WSSV infection; but until now, its function has remained obscure. We show here that ICP11 acts as a DNA mimic. In crystal, ICP11 formed a polymer of dimers with 2 rows of negatively charged spots that approximated the duplex arrangement of the phosphate groups in DNA. Functionally, ICP11 prevented DNA from binding to histone proteins H2A, H2B, H3, and H2A.x, and in hemocytes from WSSV-infected shrimp, ICP11 colocalized with histone H3 and activated-H2A.x. These observations together suggest that ICP11 might interfere with nucleosome assembly and prevent H2A.x from fulfilling its critical function of repairing DNA double strand breaks. Therefore, ICP11 possesses a functionality that is unique among the handful of presently known DNA mimic proteins.

NMR structure and dynamics of human ephrin-B2 ectodomain: the functionally critical C-D and G-H loops are highly dynamic in solution

Eph receptors and ephrins constitute the largest family of receptor tyrosine kinases with 15 individual receptors and nine ligands. Its ectodomains represent attractive targets not only for understanding fundamental mechanisms underlying axon guidance, cell migration, segmentation, tumorigenesis, and bone remodeling, but also for drug screening/design to treat cancers, bone diseases and viral infection. So far no NMR study on the ephrin ectodomains is available and as such their properties in solution still remain unknown. In this study, we presented the first NMR structure and dynamics of the human ephrin-B2 ectodomain as well as its interaction with the receptor EphB2. Strikingly, the NMR study reveals a picture different from those previously obtained by X-ray crystallography. Although in solution it still adopts the same Greek key fold, with the central beta-barrel ( approximately 30% of the molecule) highly similar to that in crystal structures, the other regions are highly dynamic and accessible to the bulk solvent. In particular, the functionally critical C-D and G-H loops of the ephrin-B2 ectodomain are highly flexible as reflected by several NMR probes including hydrogen exchange and (15)N backbone relaxation data. Nevertheless, as revealed by ITC and NMR, the ephrin-B2 ectodomain binds to EphB2 with a K(d) of 22.3 nM to form a tight complex in which the tip of the C-D loop and the C-terminus still remain largely flexible. The present results may bear critical implications in understanding the molecular details as well as designing antagonists of therapeutic interest for Eph-ephrin interactions.

A review on the morphology, molecular characterization, morphogenesis and pathogenesis of white spot syndrome virus

Since it first appeared in 1992, white spot syndrome virus (WSSV) has become the most threatening infectious agent in shrimp aquaculture. Within a decade, this pathogen has spread to all the main shrimp farming areas and has caused enormous economic losses amounting to more than seven billion US dollars. At present, biosecurity methods used to exclude pathogens in shrimp farms include disinfecting ponds and water, preventing the entrance of animals that may carry infectious agents and stocking ponds with specific pathogen-free post-larvae. The combination of these practices increases biosecurity in shrimp farming facilities and may contribute to reduce the risk of a WSSV outbreak. Although several control methods have shown some efficacy against WSSV under experimental conditions, no therapeutic products or strategies are available to effectively control WSSV in the field. Furthermore, differences in virulence and clinical outcome of WSSV infections have been reported. The sequencing and characterization of different strains of WSSV has begun to determine aspects of its biology, virulence and pathogenesis. Knowledge on these aspects is critical for developing effective control methods. The aim of this review is to present an update of the knowledge generated so far on different aspects of WSSV organization, morphogenesis, pathology and pathogenesis.

White spot syndrome virus proteins and differentially expressed host proteins identified in shrimp epithelium by shotgun proteomics and cleavable isotope-coded affinity tag

Shrimp subcuticular epithelial cells are the initial and major targets of white spot syndrome virus (WSSV) infection. Proteomic studies of WSSV-infected subcuticular epithelium of Penaeus monodon were performed through two approaches, namely, subcellular fractionation coupled with shotgun proteomics to identify viral and host proteins and a quantitative time course proteomic analysis using cleavable isotope-coded affinity tags (cICATs) to identify differentially expressed cellular proteins. Peptides were analyzed by offline coupling of two-dimensional liquid chromatography with matrix-assisted laser desorption ionization-tandem time of flight mass spectrometry. We identified 27, 20, and 4 WSSV proteins from cytosolic, nuclear, and membrane fractions, respectively. Twenty-eight unique WSSV proteins with high confidence (total ion confidence interval percentage [CI%], >95%) were observed, 11 of which are reported here for the first time, and 3 of these novel proteins were shown to be viral nonstructural proteins by Western blotting analysis. A first shrimp protein data set containing 1,999 peptides (ion score, > or =20) and 429 proteins (total ion score CI%, >95%) was constructed via shotgun proteomics. We also identified 10 down-regulated proteins and 2 up-regulated proteins from the shrimp epithelial lysate via cICAT analysis. This is the first comprehensive study of WSSV-infected epithelia by proteomics. The 11 novel viral proteins represent the latest addition to our knowledge of the WSSV proteome. Three proteomic data sets consisting of WSSV proteins, epithelial cellular proteins, and differentially expressed cellular proteins generated in the course of WSSV infection provide a new resource for further study of WSSV-shrimp interactions.

Beta-integrin mediates WSSV infection

White Spot Syndrome Virus (WSSV) is a virulent and widespread dsDNA virus with a wide range of hosts. Although remarkable progress has been made on virus characterization, however, its mechanism of infection is poorly understood. In this study, by analyzing the phage display library of the WSSV genome, a WSSV envelope protein VP187 (wsv209) was found to interact with shrimp integrin. VP187 possesses the RGD motif. The interaction between integrin and VP187 was confirmed with coimmunoprecipitation. These results demonstrate for the first time an interaction between the WSSV envelope protein and a cell surface molecule. Soluble integrin, integrin-specific antibody and an RGD-containing peptide were found to block the WSSV infection in vivo and in vitro. Gene silencing using a sequence-specific dsRNA targeting beta-integrin effectively inhibited the virus infection. These findings suggest that beta-integrin may function as a cellular receptor for WSSV infection.

Shotgun identification of the structural proteome of shrimp white spot syndrome virus and iTRAQ differentiation of envelope and nucleocapsid subproteomes

White spot syndrome virus (WSSV) is a major pathogen that causes severe mortality and economic losses to shrimp cultivation worldwide. The genome of WSSV contains a 305-kb double-stranded circular DNA, which encodes 181 predicted ORFs. Previous gel-based proteomics studies on WSSV have identified 38 structural proteins. In this study, we applied shotgun proteomics using off-line coupling of an LC system with MALDI-TOF/TOF MS/MS as a complementary and comprehensive approach to investigate the WSSV proteome. This approach led to the identification of 45 viral proteins; 13 of them are reported for the first time. Seven viral proteins were found to have acetylated N termini. RT-PCR confirmed the mRNA expression of these 13 newly identified viral proteins. Furthermore iTRAQ (isobaric tags for relative and absolute quantification), a quantitative proteomics strategy, was used to distinguish envelope proteins and nucleocapsid proteins of WSSV. Based on iTRAQ ratios, we successfully identified 23 envelope proteins and six nucleocapsid proteins. Our results validated 15 structural proteins with previously known localization in the virion. Furthermore the localization of an additional 12 envelope proteins and two nucleocapsid proteins was determined. We demonstrated that iTRAQ is an effective approach for high throughput viral protein localization determination. Altogether WSSV is assembled by at least 58 structural proteins, including 13 proteins newly identified by shotgun proteomics and one identified by iTRAQ. The localization of 42 structural proteins was determined; 33 are envelope proteins, and nine are nucleocapsid proteins. A comprehensive identification of WSSV structural proteins and their localization should facilitate the studies of its assembly and mechanism of infection.

Crystal structures of major envelope proteins VP26 and VP28 from white spot syndrome virus shed light on their evolutionary relationship

White spot syndrome virus (WSSV) is a virulent pathogen known to infect various crustaceans. It has bacilliform morphology with a tail-like appendage at one end. The envelope consists of four major proteins. Envelope structural proteins play a crucial role in viral infection and are believed to be the first molecules to interact with the host. Here, we report the localization and crystal structure of major envelope proteins VP26 and VP28 from WSSV at resolutions of 2.2 and 2.0 A, respectively. These two proteins alone account for approximately 60% of the envelope, and their structures represent the first two structural envelope proteins of WSSV. Structural comparisons among VP26, VP28, and other viral proteins reveal an evolutionary relationship between WSSV envelope proteins and structural proteins from other viruses. Both proteins adopt beta-barrel architecture with a protruding N-terminal region. We have investigated the localization of VP26 and VP28 using immunoelectron microscopy. This study suggests that VP26 and VP28 are located on the outer surface of the virus and are observed as a surface protrusion in the WSSV envelope, and this is the first convincing observation for VP26. Based on our studies combined with the literature, we speculate that the predicted N-terminal transmembrane region of VP26 and VP28 may anchor on the viral envelope membrane, making the core beta-barrel protrude outside the envelope, possibly to interact with the host receptor or to fuse with the host cell membrane for effective transfer of the viral infection. Furthermore, it is tempting to extend this host interaction mode to other structural viral proteins of similar structures. Our finding has the potential to extend further toward drug and vaccine development against WSSV.